Apparatus for monitoring the closed position of a locking gas cap

ABSTRACT

An apparatus for monitoring the closed position of a locking gas cap ( 10 ) with a magnet ( 32 ) disposed at or in the locking gas cap and a solenoid ( 42 ) disposed at the tank connection pipe ( 12 ), the locking gas cap ( 10 ) having a torque limiter ( 36 ), and the magnet ( 32 ) being coupled with the torque limiter in such a manner, that it reaches a position, in which the solenoid ( 42 ) is triggered, only when the limiting torque is reached.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for monitoring the closed positionof a locking gas cap, with a magnet disposed at or in the locking gascap and a magnetic switch disposed at the tank connection pipe.

An apparatus of this type is described in the DE 44 04 014 A1 and servesto monitor the closed position of the locking gas cap of a motor vehicleso that, when the locking gas cap is not closed or closed incompletely,a warning signal appears on the dashboard of the vehicle.

In the case of the known apparatus, the locking gas cap has a bayonetcatch and the magnet is disposed in such a manner, that it is in thevicinity of a reed switch, when the bayonet catch is locked. Dependingon the construction, the reed switch is thus either open or closed whenthe locking gas cap reaches the locked position. Preferably, the reedswitch is constructed so that it is closed in the locked position andthat an associated evaluating circuit causes a warning signal to bedisplayed when the circuit of the reed switch is interrupted.

Since the magnetic field of the magnets cannot be localized to a narrowlimited space, the position of the locking gas cap can be determinedonly relatively inaccurately according to this principle. For many tankcaps, the locking gas cap is constructed as a screw-in plug. However,even in the case of bayonet-like tank caps, screw pitch surfaces areusually provided, which ensure that the plug, in the closed position, ispressed firmly against an associated seal. The possibility thereforeexists that the locking gas cap is not turned completely into the endposition, in which the tank opening is sealed reliably and in which asubsequent loosening of the locking gas cap due to vibrations isprevented because of the frictional engagement. However, because of theaforementioned inaccuracy in determining the position, the reed switchwould also respond in such a case, so that the correct closing of thelocking gas cap cannot be indicated reliably.

SUMMARY OF THE INVENTION

It is an object of the invention to make it possible to monitor theclosed position of the locking gas cap with greater reliability.

Pursuant to the invention, this objective is accomplished owing to thefact that the locking gas cap has a torque limiter and the magnet iscoupled with the torque limiter in such a manner, that it reaches aposition, in which the magnetic switch is triggered, only when thelimiting torque is attained.

By these means, it is ensured that the magnetic switch responds onlywhen, while screwing in the locking gas cap, the limiting torque isactually reached and it is thus ensured that the locking gas cap iseffectively closed tightly and completely.

A locking gas cap with a screw-in plug and a torque limiter is describedalready in DE 196 10 471 C2. This locking gas cap has a cap, which isrotatably disposed on the screw-in plug and is provided with a handle.The torque, which is exerted by the user on the cap, is transferred bythe torque limiter to the screw-in plug. As soon as the limiting torqueis exceeded when the closed position is reached, the cap rotatesrelative to the screw-in plug. In accordance with an advantageousdevelopment of the present invention, this relative movement is used forthe purpose of transferring the magnet into the triggering position.Preferably, the magnet is held axially movable in the locking gas capand, at the cap or at the plug of the locking gas cap, inclined surfacesare provided, which convert the rotation of the cap relative to the pluginto an axial motion of the magnet. The magnet is pre-stressedelastically in the position at rest and is converted into the releaseposition only when the limiting torque is reached by the inclinedsurfaces. At the same time, the inclined surfaces and the associatedmating surfaces can be constructed in such a manner, that they can slideoff one another when the cap is rotated further after it has reached thelimiting torque. In this case, it is possible that the magnet springsback once again after it has exceeded the limiting torque and is removedfrom the release position. Preferably, this spring-back motion is,however, limited so that the magnetic switch, because of the magneticremanence of the reed contacts, nevertheless remains closed. Only whenthe locking gas cap is loosened once again or removed completely, doesthe distance between the magnets and the magnetic switch become so largethat the switch opens up. In this case, therefore, the magnetic switchexhibits some hysteresis behavior. It closes only when the limitingtorque is reached or exceeded at least once, but then remains closedwhen the magnet once again is removed further from the magnetic switch.

Alternatively, an embodiment is also conceivable, for which the magnet,in the release position, is relatively close to a magnetizable body, sothat, upon reaching the release position, it is held magnetically in therelease position and springs back once again into the position at restonly when it is screwed out of the locking gas cap.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, examples of the invention are described in greaterdetail by means of the drawings, in which

FIG. 1 shows a section through a locking gas cap when the closedposition in a tank connection pipe is reached and

FIG. 2 shows a section through the locking gas cap in a position afterthe limiting torque of a torque limiter is exceeded.

DETAILED DESCRIPTION

In FIG. 1, a locking gas cap 10 is screwed onto a connection pipe 12 ofa fuel tank of a vehicle. The locking gas cap has a screw-in plug 14 anda cap 16, which is connected rotatably with the screw-in plug and formsa handle 18. In the opening of the tank connection pipe 12, a threadedinsert 20 is fastened, which has engaged the external thread of thescrew-in plug 14. FIG. 1 shows the locking gas cap in the closedposition, in which a flange 22 of the screw-in plug, over a seal 24, isin sealing contact with the edge of the threaded insert 20.

In the interior of the screw-in plug 14, a pot-shaped inner part 26 and,further to the outside, that is, further towards the top in FIG. 1, aguiding bush 28 is disposed, in which a magnet carrier 30 is guidedaxially movably. A magnet 32 (permanent magnet) is held with holdingclaws at the magnet carrier 30 and lies within the pot-shaped inner part26. The guiding bush 28 at the same time forms an abutment for thesprings 34, which place the magnet carrier 30 and the magnet 32elastically under tension in an upwards direction in FIG. 1 in aposition at rest.

A known torque limiter 36 is effectively disposed between the cap 16 andthe screw-in plug 14. When the locking gas cap is screwed onto the tankconnection pipe, the rotational movement of the cap 16 is transferred bythis torque limiter 36 to the screw-in plug 14 until a specifiedlimiting torque is attained. This limiting torque is selected so thatthe screw-in plug 14 is then screwed firmly into the threaded insert 20and closes off the tank connection pipe tightly. The torque limiter 36is indicated in FIG. 1 merely by broken lines and is formed by springs,which are held at the cap 16 and engage a ring of notches surroundingthe guiding bush 28 (see DE 196 10 471 C2). In the state shown in FIG.1, the limiting torque has just been exceeded, so that the spring hasbeen displaced from the associated notch.

At its upper end protruding into the handle 18, the magnet carrier 30has a ring of cams 38, which are skewed in the peripheral direction andinteract with the releasing devices 40, formed in the handle 18. Whenthe limiting torque of the torque limiter is exceeded, the cap 16 turnsrelative to the screw-in plug 14 and, with that, also relative to themagnet carrier 30. The releasing devices 40 therefore slide on theskewed cams 38 and force the magnet carrier 30 downward, against theforce of the springs 34, into the release position shown in FIG. 1. Inthis position, the magnet 32 brings about the closing of the reedcontacts of a magnetic switch 42, which is disposed on the outside atthe tank connection pipe 12. In this manner, a signal is generated,which indicates the complete closing of the locking gas cap.

If the cap 16 is turned further, the releasing devices 40 slide from thecam 38, and the magnet carrier 30, under the action of the spring 34,rebounds up once again, so that it assumes the position at rest, shownin FIG. 2. In this position, the magnet is further removed from thesolenoid 42. If the magnetic switch 42 previously was closed, it remainsclosed because of the magnetic remanence in the closed state.

When the locking gas cap 10 is screwed out of the tank connection pipe12, the distance between the magnet 32 and the magnetic switch 42becomes larger, so that the magnetic switch opens up. Since the torquelimiter 36 can act only in one direction of rotation, a torque,unlimited in principle, can be transferred to the screw-in plug 14 as itis being screwed out.

Subsequently, if the locking gas cap is screwed back once again onto thetank connection pipe and has reached once again the position shown inFIG. 2, the magnetic switch 42 remains open, since the force of themagnet 32 alone is insufficient for bringing the reed contacts into theclosed position. Only when the limiting torque is exceeded once againand, at the same time, the magnet carrier 30 is moved once more into therelease position shown in FIG. 1, does the magnetic force become solarge that the magnetic switch 42 is closed once again and then remainsclosed.

In a modified embodiment, it is also possible to form the torque limiterdirectly by the cams 38 and the releasing devices 40.

What is claimed is:
 1. An apparatus for monitoring the closed positionof a locking gas cap relative to a tank connection pipe, said apparatuscomprising: a magnet mounted to the locking gas caps a magnetic switchdisposed at the tank connection pipe, and a torque limiter mounted tothe locking gas cap and coupled with the magnet in such a manner thatthe magnet reaches a position in which the magnetic switch is triggeredonly when a limiting torque of the torque limiter is reached when thelocking gas cap closes the tank connection pipe.
 2. The apparatus ofclaim 1, wherein: the locking gas cap has a plug which closes off thetank connection pipe, and a rotatable cap, which is coupled by thetorque limiter with the plug, and when the limiting torque is exceeded,can be rotated relative to the plug, and the magnet can be moved into arelease position by rotation of the cap relative to the plug.
 3. Theapparatus of claim 2, wherein the plug is a screw-in plug.
 4. Theapparatus of claim 2, wherein the magnet is held axially movable in theplug.
 5. The apparatus of claim 4, further comprising: a magnet carriermounted to the locking gas cap for holding the magnet, an arrangementfor placing the magnet under tension elastically in a position at rest,which is opposite the release position, releasing devices on therotatable cap, and cams formed on the magnet carrier for, in conjunctionwith the releasing devices, pressing back the magnet into the releaseposition.
 6. The apparatus of claim 5, wherein the cams and thereleasing devices, upon reaching or exceeding the limiting torque,permit the magnet carrier to spring back into the position at rest, andin that the position of the magnet in the position of rest and itsstrength are matched to the position of the magnetic switch in such amanner, that the magnetic switch, having been closed once, remains inthe closed state even if the magnet is in the position at rest.
 7. Theapparatus of claim 3, wherein the magnet is held axially movable in theplug.
 8. The apparatus of claim 4, further comprising: a magnet carriermounted to the locking gas cap for holding the magnet, an arrangementfor placing the magnet under tension elastically in a position at rest,which is opposite the release position, releasing devices on therotatable cap, and cams formed on the magnet carrier for, in conjunctionwith the releasing devices, pressing back the magnet into the releaseposition.
 9. The apparatus of claim 5, wherein the cams and thereleasing devices, upon reaching or exceeding the limiting torque,permit the magnet carrier to spring back into the position at rest, andin that the position of the magnet in the position of rest and itsstrength are matched to the position of the magnetic switch in such amanner, that the magnetic switch, having been closed once, remains inthe closed state even if the magnet is in the position at rest.